1. Field of the Invention
The present invention relates to an electroplated magnetic thin film made of Fe—Co alloy, a method of manufacturing such an electroplated magnetic thin film, an electroplating bath for in such a method, and a thin film magnetic head comprising such an electroplated magnetic thin film constituting at least a pole portion.
2. Related Art Statements
In a hard disk device using a thin film magnetic head, a surface recording density has been increased for attaining a large storage capacity. To this end, a width of a pole portion of an inductive type writing thin film magnetic head (said width determing a width of a record track) has been reduced and there has been proposed a pole portion having a width of sub-micron order. In such a miniaturized thin film magnetic head comprising a pole portion having such a narraw width, magnetic thin films are made of magnetic materials having a very high saturation magnetic flux density.
In a known thin film magnetic head, a permalloy consisting of Fe—Ni alloy is typically utilized. A permalloy having a very high saturation magnetic flux density of 1.5 T (Tesla) has been developed by adjusting a composition such that a content of Fe is set to 50–60 weight %. However, this value of the saturation magnetic flux density is not sufficiently high as a magnetic material for the above mentioned pole portion having a width of sub-micron order.
There has been also proposed a magnetic thin film made of a magnetic material having Fe and Co as main components. Richard M. Bozorth reported in “Ferromagnetism” that a bulk magnetic material made of Fe—Co magnetic alloy containing Fe by an amount of 49–69 weight % has a very high saturation magnetic flux density of about 2.4 T. It should be noted that a magnetic material for use in a thin film magnetic head has to be formed as a thin film, but it is difficult to form a magnetic thin film having a composition identical with a magnetic bulk.
The above mentioned Fe49–69 wt %—Co electroplated alloy has poor surface flatness and gloss and has a clouded outer appearance. Furthermore, since this alloy is liable to produce coarse crystal grains, its coercive force is extremely high. In order realize a high surface recording density, a magnetic record medium having a high coercive force is used, and therefore a pole portion of a thin film magnetic head should be made of a magnetic material having not only a high saturation magnetic flux density, but also a low coercive force in an axis of hard magnetization. Moreover, a thin film magnetic head is formed by a stack of a plurality of magnetic thin films, and therefore a magnetic thin film should have a flat and glossy surface from a view of manufacturing process.
Techniques for forming a magnetic thin film made of Fe—Co alloy have been disclosed in Japanese Patent Application Laid-open Publications, Kokai Hei 3-283013, 5-190327, 5-29172, 6-5423 and 6-36929.
In the above mentioned Kokai Hei 3-283013, an electroplated magnetic thin film made of Fe—Co alloy is described. In this electroplated magnetic thin film of Fe—Co, in order to reduce a magnetostriction to substantially zero, a content of Fe is set to about 10 wt %. Such an electroplated magnetic thin film made of Fe10 wt %—Co alloy has a saturation magnetic flux density of about 1.9 T. Although this value of a saturation magnetic flux density is higher than that of conventional magnetic thin films made of permalloys, it is still insufficient for realizing the above mentioned high surface recording density.
The above mentioned Kokai Hei 5-190327 discloses an electroplated magnetic thin film made of Fe—Co containing Rh, Kokai Hei 5-29172 shows electroplated magnetic thin films made of Fe—Co containing Pd, Cu, Pt, Au, Ag, Ir, Rh and Ru, Kokai Hei 6-5423 discloses a magnetic thin film made of Fe—Co including Cu as addition, and Kokai Hei 6-36929 describes an electroplated magnetic thin film made of Fe—Co containing Sn. These magnetic thin films made of alloys containing Fe—Co as a main component have been developed to realize control of magnetostriction, miniaturization of crystal grain, and low coercive force with laminate structure. However, since a deposition potential of Fe and Co differs from a deposition potential of a third element, an amount of a third element could not be controlled easily as compared with a binary alloy of Fe—Co, and thus it is extremely difficult to obtain an electroplated magnetic thin film having desired characteristics.
As explained above, in accordance with the increase in a storage capacity and a surface recording density of a hard disk device, improvement of performance of a thin film magnetic head is required. To this end, there has been proposed a combination type thin film magnetic head instead of an inductive thin film magnetic head performing both recoding and reading. Such a combination type thin film magnetic head comprises a stack of a recording thin film head consisting of an inductive type thin film magnetic head element for recording magnetic information and a reproducing thin film head including a magnetoresistive type element for reading magnetic information (the later element is simply called MR element).
As stated above, a magnetic material constituting a pole portion of a head core of an inductive type thin film magnetic head is required to have lower coercive force, high permeability, and high saturation magnetic flux density. Furthermore, a magnetic material having a small magnetostriction is preferably used. The most important factor of the inductive type magnetic converting element in the combination type thin film magnetic head is to increase a surface recording density. To this end, various characteristics of known magnetic materials for the inductive type magnetic converting element should be checked again and suitable magnetic materials which can realize a much higher surface recording density should be proposed, while considering a special structure of the combination type thin film magnetic head.